Process of preparing resin compositions



Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE PROCESS OF PREPARINGRESIN COMPOSITIONS Delaware No Drawing. Application April 26,- 1934,Serial N0. 722,482

3 Claims. (01. 106-22) This invention relates to a new and improvedmethod of preparing resin compositions and,

more particularly, to the preparation of composi tions comprisingthermoplastic resins of the class 5 consisting of the polymerizationproducts of acrylic and alkacrylic acids, their homologues andderivatives, said compositions being valuable for the production ofmolding powders and other uses.

1 Molding compositions in granular form must fulfill certain conditionsto be commercially acceptable. The ingredients of the compositions mustbe thoroughly blended together homogeneously to such a degree that anarticle subsequently molded from the mixture shall be of uniformcomposition and texture throughout, and of uniform color, that is, freefrom aggregates of undispersed coloring matter and from spots deficientin color. -These compositions must be in granular to pulverulentcondition to facilitate the handling. Customarily in molding shoppractice the charges for the individual molds are made up by passing thegranular compositions through a preforming or pelleting machine whichautomatically measures out a predetermined weight of the material andcompresses the loose granular material into a hard and durable preform,this preform being much more readily loaded into the die than would bethe material in its granular form. 1

Not only must the molding composition be in granular form but,'in orderto satisfactorily handle it in the preforming machines, it must not betoo voluminous, that is to say, the granular material must have asufiiciently high bulk density, by which term is meant the apparentdensity of a granular molding compound in an untamped, loose condition,generally expressed in weight per unit volume as in the mixed term gramsper cubic 40 inch. The granular material must be in such condition as tofeed readily by gravity from the hopper to the cavity of the pelletingmachine and must not contain an undue proportion of fines which tend tocause the jamming of the plunger in the cavity of the pelleting machineby building up in the narrow clearance provided between them. Moreover,the granular material must not contain any individual particles ofcomparatively large size, as then the operation of the pellet- 5 ingmachine will be defective in that the automatic device which levels offthe individual charge of material in the cavity will not accuratelylevel material containing very coarse particles.

Heretofore methods have been proposed for the 55 preparation of moldingcompositions having a base of resins of the type herein underconsideration, which compositions are usable as molding compounds andwhich also may be worked up into useful products by other means. Ingeneral, the methods heretofore known for the prep- 5 aration ofhomogeneous compositions of this type are uneconomical for commercialoperation and/or involve subjecting the plastic masses to excessivetemperatures or other conditions whereby the properties of the finishedcomposi- 10 tion are deleteriously afl'ected.

An object of the present invention is to provide a simple andeconomicalprocess for producing homogeneous compositions of thermoplastic resinsof the class consisting of the polymeriza- 15 tion products of acrylicacids and alkacrylic acids, their liomologues and "derivatives, inconjunction with auxiliary ingredients, which compositions are suitablefor various purposes and in particular for use as molding powders. Afurther ob- 2o ject is to provide a process whereby such compositionsmay be produced in homogeneous granular form having the characteristicsof bulk density and screen analysis which would make them suitable foreconomical handling in the mold- 25 ing'industry. A still further objectis to provide a process wherein the obvious drawbacks of the heretoforeknown processes are avoided.

The above objects are accomplished according to the present invention bykneading a thermo- 30 plastic resin from the class consisting of thepolymerization products of acrylic and alkacrylic acids, theirhomologues and derivatives, usually in conjunction with auxiliaryingredients and substantially in the absence of volatile solvents, 35 incomminuted form in a. masticator mixer under positive pressure until ahomogeneous, fully colloided, continuous plastic mass is obtained.Ordinarily the plastic mass thus obtained is allowed to cool to roomtemperature and then broken 40 down into granular form to makeit'suitable for use as a molding powder, although it may be used in theplastic arts in other form, as will be understood by those skilled inthe art.

The invention is broadly applicable to thermo- 5 plastic resins of theclass consisting of the polymerization products of acrylic andalkacrylic acids and their derivatives and homologues, such as thenitriles, amides, substituted alkyl and substituted aryl derivatives ofthe acids and, particularly, the esters of the acids such as the alkylesters of acrylic acid, methacrylic acid, ethacrylic acid, and thehigher homologues. Specific resins included are the polymerizationproducts of methyl and ethyl methacrylate and methyl and whosepreparation is disclosedtin, Rowland Hill,-

application serial iNo'. 41,113; me November 3; 1932. Thesethermoplastic resins'need not be one hundred percent polymers of themonomer from which they are made and ordinarily contain some monomer.The presence of anappreciable" proportion of monomer, for example, 10-45p'arts,

will increase the thermoplasticlty of; .the 1'esii r and, for certainpurposes, may be, found, advanr;

tageous.

It has been discovered that the severe kneading action obtainable in amasticator mixer is peculiarly and unexpectedly well adapted for form-.,

ing commlnuted resins of the type described above into compacted,-ful1ycolloided, continuous plastic masses and at the same time homogeneouslyincorporating vtherein plasticizers, coloring matter, fillers, and thelike, in a remarkably short period of time without employing volatilesolvents or excessive heat. In fact, even plasticizers may be omitted,if desired, and the use of exceptionally large amounts of plasticizersto offset the absence of volatile solvents or temperatures so highthatthe plastic mass may be injuriously affected, is absolutely unnecessaryinthe process of the present invention, thereby sharply distinguishingthis process from those heretofore known using other types of mixers.

Masticator mixers are well known in the art, the so-called "Banbury?mixer being a prominent example. The masticator V mixer comprises aworking space within which rotate the mixing blades, ordinarily twoinnumber, which are designed to have very small clearance with the wall ofthe working space. The mixer comprises further a ram, actuated bycompressed air, or the like, which bears down upon the charge of ma;-terial being mixed and forces the material to pass through the narrowclearances above mentioned with the result that the material issubjected to a very severe masticating action quite peculiar to thistype of apparatus. The pressure ram could be replaced by any equivalentmeans for insuring that the plastic mass being kneaded is forced downbetween thev blades of the mixer and the wall of the working space,rather than merely riding around with the blades and avoiding thekneading action. The term under positive pressure" is used herein in itscustomary sense in this art, namely, that a pressure ram or equivalentdevice, is forcing the mixture down into the narrow clearances betweenthe blades of the mixer and the adjacent walls so that the material issubjected to a very severe kneading action. In the specific examplesgiven hereinafter a pressure of 10-50 pounds per sq. in. of ram surfacewas exerted on the pressure ram but it is to be understood that there isnothing critical about the pressure exerted on the ram and,consequently, upon the material in the mixer, so long as the material isprevented from merely riding around with the blades of the mixer andavoiding kneading action. The pressure on the ram. or equivalent device,will undoubtedly vary widely depending upon the size and design ofmasticator mixer which is employed.

In carrying out the present invention, the resin in question incommlnuted but not necessarily pulverulent form, together with anyauxiliary ingredients in desired proportions, is introduced into amasticator mixer in sumcient quantity so aosenos I that the workingspace of the mixer is filled to such a point that the pressure ram ofthe mixer will operate to exert positive pressure upon the contentsduring the kneading action and thus force-thematerialinto thenarrowclearances as desired. The mixer is see-law an, with the pressureram in operating position to exert positive pressure upon the masswithin the mixer.

The severe rnasticating action elects a homofgenization of tire-mixtureand also produces considerable heat, as a result of internal frictionwithin-the material,, so that the mass ultimately reacheswhat isknown tothe art as a colloided #:condition. This "colloided mass is dense,tough, and horny and in the absence of pigments, fillers,

and the like, is substantially transparent in ap- .pearance., It isdischarged from the masticator mixer in the form of granules and lumpsof various sizes which, preferably after being cooled,

maybereduced by grinding to a granular form suitable for moldingpowders.-

ahor'nogeneous colloided product,;is the remarkably short periodrequired-to knead, in amastie cator mixer these resins to obtain acompletely homogeneous and colloided mass. 1 The operation is to bemeasured in minutes and rarely does the kneading action have to beprolonged over 15 minutes, more usually a period of about 5 minutesbeing ample.. v i g The following examples illustrate specificembodiments of the invention, parts being given by weight:-- n v IExampZe 1.A mixture of 100 parts of polymerized methyl, methacrylateresin, 26 parts of diamyl phthalate as a plasticizer therefor, and 2parts of stearic acid as a mold lubricant, was loaded into a Banburymixer in such quantity that, when the, blades were set in motion and.the pressure ram brought. into operating position, the ram would exertpositive pressure upon the charge so as to force it into vthe clearancesbetween the blades and the walls of the .mixer. The blades were set intomotion, the pressure ram brought into operating position and the mixingcontinued until the charge had reached the condition of a homogeneous,compacted, colloided mass. The processing required .5 minutes and theScreen analysis On 10 mesh 27.1

100 0.2 Through 100 0.1

The granular material was molded in a suitable die by the application ofa temperature of 150 C. and a pressure of 2500 pounds per square inch ofprojected area, followed by a cooling before the article was removedfrom the die. The article was homogeneous in appearance and uniformlystrong and evenly textured.

Example 2.- --A mixture of 100 parts of polymerized methylmethacrylateresin and 2 parts of stearic acid was loaded into a Banburymixer and processed in the same manner as in Example 5 1. A homogeneous,compacted, completely colloided mass was obtained when the temperatureof thecharge had reached about 171 C. which occurred after 14 minuteskneading. In this example no plasticizer was used, thus necessitating asomewhat longer kneading cycle than in Example 1, and an appreciablyhigher temperature.

The resulting mass was cooled and granulated by grinding. An article ofhomogeneous appearl5 ance and uniformly strong was obtained by moldingthis material by the application of a temperature of 170 C. and apressure of 4500 pounds per square inch of projected area, followed bycooling and removal of the article from the die.

0 Example 3.-A mixture of 100 parts of polymerized methyl methacrylateresin, 11.3 parts of tributyl phosphate as a plasticizer therefor, and0.6 part of stearic acid was loaded into a Banbury mixer and worked asin Examples 1 and 2.

A molding powder was obtained which could be molded into articles ofsatisfactory appearance and strength.

Example 4.-A mixture of 100 parts of polymerized methyl methacrylateresin, 5.3 parts of diamyl phthalate, and 0.5 part of stearic acid wasloaded into a Banbury mixer and treated as in the preceding examples,the resulting composition being satisfactory for use as a moldingpowder.

The above examples are merely illustrative of the invention whichbroadly includes kneading in a masticator mixer under positive pressureany one or more of the resins disclosed, with or without otheringredients, until a homogeneous, compacted, colloided mass is formedwhich may be broken down into granular form for use as a molding powder,or may be subjected to known plastic processes such as rolling,slabbing, cake pressing, extruding, dope making, and the like.

The resin preferably should be in fairly finely divided form. althoughnot necessarily 'pulverulent, in order that homogenization of thecomposition may not be unduly delayed by the need of breaking downcoarse particles. Obviously the resin may very well be used in the formof coarse particles if its physical condition is such that it would bepractically immediately broken down into finely divided form uponsetting the mixer in motion.

Auxiliary ingredients may be added to the resin such as would be usedfor the ordinary purpose of modifying the resin with respect to color,rigidity, mechanical strength, electrical properties, and the like, tomeet the requirements of use of the ultimate product made therefrom. In

ordinary commercial operation coloring ingredients and plasticizerswould be used. The coloring ingredients may be pigments or dyestuffs andit has been found that no special provision is necessary for preliminarypreparation of coloring ingredients. Usually the mixture to beintroduced into the Banbury is formed by adding the ingredients to someordinary light construction mixing device to give a preliminary mixingand it has been found that, if coloring matter is merely introduced in adry condition into this preliminary mixer, the coloring matter will beuniformly distributed throughout the plastic composition at the end ofthe kneading cycle in the masticator mixer. Certain pigment colors aremore refractory in'this respect, tending to resist dispersion by thekneading action and to remain in agglomerated form, distributedthroughout the mass, so as to produce a nonuniform or speckledappearance. When dealing with ,5 such pigments, or, for example, whendealing with a plastic mixture which is so readily kneaded to anotherwise homogeneous colloided condition as to allow insuflicient timefor the dis-- persion of the coloring matter, it is desirable to 10subject the coloring matter to a special preliminary treatment topromote its dispersion, such type such as cyclohexyl butyl, benzyl butylor.

butyl lauryl phthalate; esters of dibasic acids, such as the ethyl,propyl, isopropyl, butyl, isobutyl, cyclohexyl, methyl cyclohexyl orben'zyl esters of succinic, fumaric, tartaric, adipic, methv30 yladipicand sebacic acids; esters of monobasic acids, such as the butyl,isobutyl, cyclohexyl, methyl cyclohexyl, benzyl or lauryl esters oflauric, laevulinic, benzoic, benzoyl propionic and benzoyl benzoicacids; esters of polyhydric alco- 35 hols, e. g., glycol and glycerol,such as glycol benzoate, glycol laevulinate, triacetin, tripropionin andtributyrln; substituted toluene sulphonamides, such as ethylparatoluene-sulphonamide; substituted amides, such as tetraethyliiophthalamide, tetrabutyl succinamide, tetrabutyl adipamide, tetraethylphthalamide; hydrocarbons, such as dixylyl ethane; halogenatedhydrocarbons, such as chlorinated diphenyls and dichlordibenzyl; ethercompounds such as dicresoxy 5 ethyl ether; and phosphates such astriphenyl and tricresyl phosphates.

Fillers such as china clay, terra alba, gypsum, asbestos, wood flour,cotton flock, and the like; effect materials such as bronze powders,pearl 50 essence, and the like; lubricants such as stearic acid,metallic soaps, e. g., aluminum palmitate and calcium stearate; andwaxes, e. g., carnauba and candelilla wax; and other miscellaneousingredients such as natural resins, other synthetic 55 resins, and thelike, may be included in the composition to be processed according tothe present invention. The inclusion of such ingredients and theproportions thereof will be determined by the particular propertiesdesired in the fln- 60 ished composition and not with relation to theworking of the process of the present invention.

The homogenization of the mixture introduced into the masticator mixeris directly a result of the severe masticating action to which it issub- 65 jected and the degree of homogenization is primarily a functionof the time of mixing, although it is true that homogenization isfacilitated by the softening of the resin which results from the heatdeveloped during the kneading cycle. 7

On the other hand, the colloiding of the mass is dependent primarilyupon the temperature to which it is carried and very little upon thetime of mixing. In order that any given mixture shall reach a colloidedstate it is, in general, requisite 75 temperature; The. ease with whicha given turelis rendered omo'ge'neous' will be dept-p11 h ch 1 a :n en,more 1 w l r a f e'ae a state, under. given conditions as oi *tem (orconversely, the temperature reand proportion er the pmsticiz'en upon thero:

portiomot inert ingredients present, (e; g., e'r's', et ce't'era) andupon the charac' teristic influencefiofany' other ingredient whichmaybeinvolvedfi Accordingly the process maybe controlled, ;-by suitableheating "or" cooling of the mixing apparatus, by'fcontrol-o! the smear'the'charge put into use that "homogenization and the de-' velopment ofthe colloided'mass" will be efl'ected in a nunimum time and at'aminimum'ternperature. Ii',ior example, under certain conditions the masstends 'toheatup to a temperature beyond that required for the formation01 a colloid but in a period of time insuiiicient to effecthomogenization, the obvious remedy, in order to avoid damage 'to .themass which might result from excessive temperature, is to start theoperationwith the mixer at a lower temperature, or to apply coolingm'eans during'the process ing, so that an excessively high temperatureis not reached before homogenization is eflected. In general, the heatrequired for effecting colloiding is derived for the most part from theinternaltrlction of the plastic mass and the application of heat fromexternal sources is frequently unnecessary. I

On the other hand, it, for example, under certain conditions the masstends to become fully homogeneous before colloidalization, then themixer may be heated initially or during the processing in order that theminimum temperature for colloiding the particular mixture may be quicklyreached and the colloiding speeded up so that it will be efiectedvatapproximately the same time the material becomes substantiallyhomogeneous. I

The homogeneous, fully colloided material as removed from the masticatormixer is, of course, at an elevated temperature, usually at least 100 C.In order to reduce this material to granular form for use as a moldingpowder it is preferred to first cool the material down, as thisfacilitates the grinding. The material may be reduced to granular formby any known grinding means such as a hammer mill, a rotary mill, 9.three-roll mill, or the like.

An advantage of the present invention is that it provides a process inwhich the use of volatile solvents is entirely unnecessary and,accordingly, the process is free from the expense arising from thecharactenand initial neness of, the ingredients. The ease with again,ass

los's of solvent and oi recovering solvent.- In

the present-*process-f the" ot "vola'tile solvents may be dispensed witheven whjeri'theplasticize'r is present "in only proportions or"absentaltogether,"as illustrated in Example 2;- -A fur-i theradvantageof --thepresent process "is that it may 7 be 1 carried out at a;moderate tempera-ture, particularly where? plasticizers 1 are 1 employedin the usual amounta thus avoiding a serious objjee-r tion to heretoioreproposed' processes wherein the out in a traction oi the'tirnewh-ich=would be required for 1 the preparationor homogeneous, col

loided masses by-or'dinary mixing means and thus further minimizesexposure of the mat'erial' to, heat and,'-o i course,-shortehs theprocessing cycle which makes possible a large production perday per unitwith correspondinglylow labor cost. Upon-breaking down thecolloidedplastic mass producedaccording tothe present processpa granular materialof high bulk density and satisfactory screen analysis is obtained, 1.-e.,:a highly satisfactory material for use in molding shop practice.Also the present process provides means of making a transparent plasticmass free from discoloration, dirt, orany contamination which wouldcause haze; I

As manyapparently widely different-embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific[embodiments thereof except as definedin the appended claims. a

We claim: V

1. Process of preparing'molding compositions, comprising kneading, inthe absence of volatile solvent, hard, dry, comminuted polymerizedmethyl methacrylate resin in a masticator mixer under positive pressureuntil a homogeneous, compacted, colloided mass is obtained, removingsaid mass from the mixer and breaking itdown into granular form.

2. Process of preparing molding compositions comprising kneading, in theabsence of volatile solvent, 9, mixture comprising hard, dry, comminutedpolymerized methyl methacrylate resin and a plasticizer for said resin,in a masticator mixer under positive pressure until a homogeneous,compacted, colloided mass is obtained.

3. Process of preparing molding compositions comprising kneading, in theabsence of volatile solvent, a mixture comprising hard, dry, comminutedpolymerized methyl methacrylate resin, a plasticizer for said resin, amold lubricant, and a pigment, in a masticator mixer under positivepressure until a homogeneous, compacted, colloided mass is obtained,removing said mass from the mixer and breaking said mass down intogranular form.

MAURICE L. MACHT. ALAN F. RANDOLPH.

